Histopathological changes in the skin and gut mucus layers of rainbow trout (Oncorhynchus mykiss) challenged with Ichthyophthirius multifiliis inactivated by gamma rays and formalin

Ichthyophthirius multifiliis, a protozoan parasite, is a significant problem for fish farmers and Aquarium fish worldwide. This study aimed to evaluate the immunization of rainbow trout with gamma-irradiated, formalin inactive, and live theronts of I. multifiliis. In this study, fish were exposed to gamma-irradiated, formalin-inactivated, and live I. multifiliis theronts. Then, the histopathological changes in the mucous layers of the skin and intestines were studied after 7 and 14 days of exposure. Although no significant morphological changes were observed in the skin and intestines of the treated fish, the number of skin goblet cells increased significantly in fish treated with formalin-inactivated, gamma-inactivated, and live trophonts on 7 and 14 days. Compared to the negative control group, an increase in epidermal thickness on the skin was observed in fish challenged with formalininactivated, gamma-inactivated, and live trophonts. The numbers of mucous cells/total enterocytes in the intestinal epithelium of fish exposed to gamma-irradiated, formalin-inactivated, and trophonts live were higher than in non-infected fish. Moreover, a significant increase was found in the mucous cell numbers of the pyloric fold in treated fish with gamma-irradiated and formalin inactive trophonts at the first and second weeks. The results showed that the gamma-irradiated trophonts and formalin inactive trophonts could be safe for use in rainbow trout against I. multifiliis